1. Field of the Invention
The present invention relates to a channel encoding/decoding method in wireless communication systems, more particularly, to a serial concatenation of space-time codes applicable to communication systems with multiple antennas.
2. Description of the Prior Art
The serial-concatenation of space-time codes uses a space-time code as the outer code and uses a recursive systematic convolutional (RSC) code as the inner code. For wireless communication systems using several transmission and reception antennas at the transmitter and receiver, respectively, a method of corresponding a recursive systematic convolutional code to the respective transmit antenna as the inner code was proposed. This method was designed to increase the coding gain of the overall space-time code, and decoding is performed separately for the respective RSC code at the receiver. In the paper entitled “Improved space-time codes using serial concatenation” in “IEEE Communications Letters”, June, 2000, the same number of RSC codes as that of the transmission antennas are used as the inner code, and the decoding for the inner code is performed separately for the individual codes by using an inner decoder corresponding to the respective RSC code. In the case of using the multiple codes as the inner code and decoding them individually, each decoder for decoding the inner code has 2nq trellis branches per state and the total number of the trellis branches that must be computed so as to perform the decoding for Nnq bits in one iteration becomes (the state number)×N×2nq. Although such individual decoding method has a simple decoding procedure and low complexity, it has low decoding efficiency, that is, low performance.
On the other hand, a relatively complex decoding method has the same encoding procedure as that of the above-mentioned method, but a combined decoding is performed for all the RSC codes. In the paper entitled “MIMO iterative decoding of serial concatenation using space-time trellis codes” in “Electronics Letters”, February, 2002, the same number of RSC codes as that of the transmit antennas are used as the inner code, and the decoding is performed by combining the RSC codes into a single code and decoding the combined code. In the case of using the multiple codes as the inner code and jointly decoding the combined code, the total number of trellis states for the combined code increases to (the state number of a single encoder)N, and each trellis state has 2Nnq trellis branches, thereby the total number of the branches that must be computed so as to perform the decoding of Nnq bits in one iteration becomes (the state number)N×2Nnq. This joint decoding method is highly efficient, but has a severe disadvantage in terms of hardware implementation because the complexity thereof increases exponentially with increasing the number of transmit antennas N.